1. Field of the Invention
The invention relates to a microphone system and more particularly to a microphone system which includes a microphone and a pair of dishes which channel the sound past the microphone.
2. Brief Description of the Prior Art
Various microphones and microphone systems have been developed over the years in an attempt to more accurately capture sound at a distance for both indoor and outdoors applications. Pressure microphones, such as disclosed in U.S. Pat. No. 4,361,736 to Long and Wickersham, dramatically improved the technology, however, problems were still apparent.
U.S. Pat. No. 4,436,966, issued to Botros uses dishes with the sound being received within the concave portion of each of the two dishes to provide bi-directional reception. As the space between the dishes is a null region, the dishes can be in contact with one another without any loss of sound. In the Botros system, the microphone is positioned to respond to the sound coming into the concave portion of each dish, capturing the sound at the apex of the dishes. The Botros dishes can be a portion of a small diameter sphere, or ellipse, with little concern as to depth of the dish. Conversely, in the disclosed microphone enclosure, the angle of the waveguide must be shallow.
U.S. Pat. No. 4,831,656, to Southern et al discloses and claims an angle of about 22 degrees between a flat reflector plate and a cone. According to the ""656 patent the predetermined 22 degree angle of the opening between the cone and the reflector plate controls the microphone""s environment by deflecting the sound waves produced by conversations into the microphone mounted within the aperture of the cone. As a result of this design, sound waves enter the microphone directly, causing the microphone to produce a significantly higher electrical output in the voice frequency range. The ""656 patent further notes that the angle between the cone and reflector plate also produces uniform directional characteristics for the microphone. The 22 degree opening from the sides of the unit is the same at any point in a 360 degree plane creating a horizontal pattern that is uniformly radially directional.
Commercially available PZM microphones from CROWN (Model SOUNDGRABBER U.S. Pat. No. 4,361,736) or RADIO SHACK, and PHONIC EAR (Model AT-560-72-3 U.S. Pat. No. 4,831,656) have been used with unsatisfactory results.
Parabolic microphones have also been used to achieve long range pickup but do so in a very narrow directive pattern. These microphones are also by necessity large. They are impractical then for indoor conference and classroom applications, and outdoors only useful where directivity is desired.
Similarly shotgun microphones are commonly used in long-range pickup situations. They must be used in a large open area to function; they are highly directional, and often too large to be of use in classrooms or conference rooms. As shown in comparisons the instant invention has a much higher acoustic gain than a shotgun microphone.
The instant invention is capable of matching parabolic range in any pickup pattern variable to 360 degrees in a radial pattern. Additionally the instant invention can match parabolic range in a package less than half the size.
The disclosed invention therefore provides a microphone system having a sensitive, variable radial pickup pattern, which overcomes prior art shortcomings.
The acoustical system of the invention converts sound waves into corresponding signals for use in acoustic data storage and/or driving a speaker. The conversion is only limited by available technology, and is most typically a conversion from sound to electrical signals. The system is equally applicable to a system which could directly convert the sound to laser beams or magnetic fields, or other form which is capable of being recorded in a data storage medium. Magnetic tapes are commonly used for this purpose, but computer type disks can also be used for the storage of data. The form into which the sound is converted, whether it be optical or electrical, or some other form, is not narrowly critical.
The system includes a housing which is formed from a pair of guide members. It is believed that the pair of guide members act as a wave guide, but an understanding of the functioning of the invention is not dependant the exact theory of operation.
A first guide member is positioned proximate a second guide member, and is shaped relative to the second guide member, such that the distance between the first guide member and the second guide member, decreases in the direction of travel of the sound wave, that is, from the outer peripheral edge to inner region. The space between said first guide member peripheral edge and said second guide means peripheral edge forms a sound wave entrance port.
The transducer is positioned proximate the inner region between the two guide members, and is positioned to be responsive to sound waves which travel downstream, from said entrance port, past said transducer. It is essential that the sound waves continue to travel past the transducer, rather than being reflected back in the upstream direction.
That is, the space between the first guide member and the second guide member forms a sound channel, which extends from the sound wave entrance port, at least to a position past the transducer, such that sound waves do not substantially reverse direction and travel toward said sound wave entrance port. Sounds waves enter the system and continue in a directionally unaltered course, until they pass out the opposite end. Preferably, each of said first guide member and said second guide member, is a dish having a convex shape.
In one embodiment, each of the guide members has a peripheral edge which extends 360 degrees, thus producing an acoustical system which is radially directional. In this form, the guide members are convex dishes, and the transducer is position essentially at the center of the dishes.
Where the acoustical system employs a pair of convex dishes, the sound channel is an open, 360 degree channel, in which sound waves enter the sound channel, travel past the transducer and continue to travel in the same direction until they exit the system, thereby forming an radially directional acoustical system.
In another embodiment, a pair of spaced apart side walls extend from, that is, between, the first guide member and second guide member, and from the sound wave entrance port toward said transducer. The first guide member, the second guide member and the pair of side walls, in combination, form the sound channel, and thereby forming a limited direction acoustical system. Looking radially outward, the guide members, are arcuate, that is, in the form of a segment of a pie. Phrased another way, the sound channel, is arcuate, with the directionality of the acoustic system corresponding to the angle of the arc of the sound channel.
In the limited direction acoustical system, a sound absorber is positioned down stream of the transducer to substantially preclude sound waves from reversing direction and traveling past said transducer toward said sound wave entrance port.
The transducer is positioned within said channel, such that said transducer is activated normal to the direction of travel of said sound waves. That is, the transducer is positioned such its active surface, typically a diaphragm, is at a right angle to the direction of travel of the sound waves. The term sound waves, as used herein, is intended to be inclusive of pressure waves, which later term may more accurately define the wave form within the sound channel. Additionally, the sound channel, is understood to operate as a wave guide, but the scope of the invention is not limited to any particular theory of operation. Essentially, the invention is the conversion of sound waves into corresponding signals of another form, as for example, electrical signals. The steps of the invention include guiding sound waves within a channel having a progressively decreasing cross-sectional area, from a channel entrance past a sound wave transducer, and precluding sound waves from re-traveling in the channel, from the transducer toward the channel entrance. This is not intended to mean that the system cannot be an open system in which first sounds waves enter in a first direction and continue until they exit at the opposite end, with other sound waves entering the exit of the first sound wave and exiting at the first sound waves entrance point. A critical point, is that sound waves do not bounce or reflect back, that is, reverse direction, and exit via their own entrance point.
This aspect of the invention can be achieved by limiting sound waves entering the channel, to waves travel from a predetermined area, and absorbing sound waves which have traveled past said sound wave transducer. The sound waves are precluded from re-traveling in said channel, from transducer toward the channel entrance.